Nanowires (NWs) moved in the focus of the nanoscience community and gained increased interest because they are promising candidates as building blocks of future MOSFETs and  quantum devices. In particular Ge-NWs has become a favourable material, due to the high carrier mobility, enabling high performance devices, and the large exciton Bohr radius, favouring quantum confinement effects. Controlling the properties of NWs especially conductivity is therefore a crucial issue. We explored a novel FIB based implantation method modulating the conductivity of such Ge-NWs by orders of magnitude without the need for thermal annealing.

The NWs are grown using a VLS process. To assure a low contact resistance, the nanowires are contacted with Cu and by controlled heating of the Ge nanowire to 310°C, the formation of copper-germanide phase is induced. This process leads to copper-germanide/germanium nanowire heterostructures with atomically sharp interfaces. With in-situ SEM observation of the Cu diffusion the Ge channel length can be controlled as well.

By FIB implantation of Ga at room temperature a maximum conductivity increase by a factor of 1000 was observed at an ion fluence of 6.25x10¹² cm^-2. HRTEM analysis shows that the crystalline core of the nanowire is preserved. The conductivity increase is discussed by enhanced dynamic annealing.

The application of this technique on top-gated NW-MOSFETs revealed a large performance increase of these devices.

Further improvements in our methods, especially narrowing the Ge gap of the nanowire, may lead to single ion detection.